A high-purity longitudinal needle-shaped magnetization field produced in a uniaxial crystal

Based on the Richard-Wolf vector diffraction theory and the inverse Faraday effect, a method for generating high purity longitudinal needle-shaped magnetization fields in uniaxial crystals is proposed for the first time. In this method, the inverse radiation of the electric dipole in the uniaxial crystal is used to construct the optimized entry pupil light field through the multi-parameter regulation of the number of electric dipole pair N and its array, and then the magnetization field of the desired target is obtained by forward tightly focusing. The simulation results show that when N=1, the focal length of the magnetic field generated in the uniaxial crystal increases by 1.4 times and the lateral resolution increases by 5% compared with that in the isotropic medium. It can be further seen that when N=2 and N=3, with the increase of the number of electric dipole pairs, the focal length of the needle magnetic field generated in the uniaxial crystal increases by 10%, and the lateral resolution increases by 18%. The purity of the needle magnetic field gradually increases to 1 as the magnetization field profile surface value changes from 0.1 to 1. Especially when N=2 and the contour surface value is 0.1, the magnetic field purity is as high as 0.95. The results provide a feasible scheme for generating the longitudinal magnetization fields with higher purity and longer focal length in anisotropic media, and also provide theoretical guidance for selecting optimized pupil beams in practical applications such as all-optical magnetic recording, atom capture and lithography.